In an atom, the order of filling up of the orbitals is governed by

1. The order of filling up of the orbitals in an atom with electrons is primarily governed by the Aufbau principle. 2. The Aufbau principle (German for 'building up') states that electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels (e.g., 1s is filled before 2s, which is filled before 2p). 3. Heisenberg's uncertainty principle deals with the impossibility of simultaneously knowing the exact position and momentum of a particle. 4. Hund's rule states that electrons will singly occupy degenerate orbitals before pairing up. 5. Pauli's exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers (meaning an orbital can hold a maximum of two electrons, and they must have opposite spins). While Hund's rule and Pauli's principle also influence electron configuration, the overall sequence of orbital filling follows the Aufbau principle.